This invention relates to a multi-battery operating system for automotive vehicles that provides improved fuel economy and reduced emissions during operation and during starting, more particularly a three battery system having a start battery for starting the vehicle, a run battery for providing the vehicle load and accessory current, and a storage battery for preheating a catalytic converter during starting.
In the normal operation of an automotive vehicle, a fully charged six cell battery having between 2.05 and 2.1 volts per cell (hereinafter referred to as a xe2x80x9cstartxe2x80x9d battery) is used to start the engine and to operate accessory loads when the engine is not running. The conventional start battery is well suited to provide large start currents to the start motor on the order of 150 to 250 amperes.
The start battery is provided with thin plates between its individual cells that provides for a rapid, large current, shallow discharge during vehicle start. Unfortunately, the start battery cannot be deeply discharged in a repetitive manner without damaging the thin cell separator plates.
It has long been the practice to provide an alternator driven by the engine that can be used to recharge the start battery after vehicle start and provide current to both the vehicle run and accessory loads. It has also been the practice to maintain the alternator charging voltage at a nominal value of 14.0 volts at an ambient temperature of 85 degrees F. The nominal value is raised to 14.6 volts at minus 20 deg. F. and lowered to 13.6 volts at 140 deg. F. This provides adequate charge current as a function of ambient temperature and thereby extends battery life.
A voltage regulator is used to inject a controlled current into the alternator rotor. This in turn provides a controlled current in the stationary (stator) field coils. This in turn yields the rectified dc output voltage required for battery recharge after start and to supply the required vehicle load currents.
It has been realized by the inventor that the conventional operation of a start battery and alternator based electrical system of an automotive vehicle wastes energy. First, the alternator requires the engine to provide fuel consuming torque to operate the alternator at a nominal value, e.g., a 14.6 volt dc output level, in order to recharge the start battery and provide the required current to the vehicle loads. Second, the vehicle electronic circuits contain power consuming voltage regulator circuits that reduce the alternator output voltage to a 12 or 5 volt level. Third, the alternator places a mechanical torque on the engine as a function of the alternator output voltage and the current drawn to supply the load requirements and to charge the start battery. The fuel consumed by the engine to overcome the alternator counter torque is an unnecessary expense. Fourth, the vehicle engine and alternator are substantially less than 100% efficient and consume a correspondingly greater amount of fuel.
In addition, the inventor has realized that if the state of charge of the vehicle batteries are reliably and accurately determinable over their useful life it is possible to control the alternator output voltage, as required, either to charge the vehicle batteries or to allow one or more batteries to provide all the current required by the vehicle loads.
It is a further object of the invention to increase alternator output voltage during deceleration of an automotive vehicle, thereby using vehicle momentum to provide an increased torque load that is used to charge a battery.
It is another object of the invention to turn off selected vehicle accessory loads when the vehicle is parked and to turn off selected vehicle accessory loads when the state of charge of the battery providing current drops below a selected level.
It is another object of the invention to provide a storage battery for providing the current required to heat an electrically heated catalytic converter (EHC) during or prior to vehicle start when the engine temperature is below a selected level.
In accordance with the present invention, apparatus, systems, and methods are provided for providing sufficient electrical power to start and run an engine, to reduce the energy expended and fuel consumed and associated emission by-products in starting and running the engine, and optionally in operating a battery charging device to maintain a sufficient charge on each battery for the range of operating load conditions.
One aspect of the invention concerns a battery charging and run system for starting the engine of an automotive vehicle and operating the electrical loads of the automotive vehicle with improved fuel economy.
One embodiment of this aspect of the invention concerns a battery charging system for an automotive vehicle having:
a start battery for use in starting the vehicle engine;
a run battery for operating the vehicle accessory and non accessory loads;
a battery charging device, such as an alternator, having a controllable output voltage when the vehicle is running;
a first BSOC channel for monitoring the state of charge of the start of battery;
a second BSOC channel for monitoring the state of charge of the run battery; and
a first circuit, such as a voltage regulator, for controlling the output of the battery charging device to provide one of a first output voltage that varies in a first range as a function of ambient temperature when the sensed start battery state of charge level is below a first charge level and a second output voltage when the battery state of charge level is above the first charge level, a third output voltage to recharge the run battery when the run battery state of charge is below a second charge level, and a fourth output when the run battery state of charge is above the second charge level.
Preferably a switch is provided to switch the start battery out of the system after it is recharged. The switch is responsive to the sensed state of charge of the start battery and open circuits the start battery upon reaching the first charge level.
In operation, the start battery is employed to start the vehicle engine. Its state of charge thus falls below the first charge level (corresponding to the prestart charge level). This causes the control circuit/voltage regulator to control the battery charging device to provide a first output voltage to recharge the start battery, e.g., between 16.4 and 13.6 volts dc, according to the ambient temperature in the conventional manner.
When the sensed state of charge of the start battery is at the first charge level, the control circuit/voltage regulator may then control the battery charging device to provide the second output voltage level to maintain a full charge on the start battery. In a preferred embodiment, the switch is configured to respond automatically to the start battery state of charge returning to the first charge level and switch the start battery out of the charging system in a fully charged state. Alternatively, the switch may be manually operated by the operator who acts in response to a prompt, such as a light, audible tone, or battery state of charge display.
When the start battery is switched out, the two battery system then may operate in one of two modes. In the first preferred mode of operation, the automotive vehicle electrical load is run off the run battery entirely. In this mode, once the start battery is switched out (and, as described below, an ECH battery is switched out), the control circuit controls the battery charging device to provide the fourth output by reducing the field current until the bridge rectifier diodes become back-biased. When the control circuit is a controllable voltage regulator, the battery charging device is an alternator, and the voltage regulator output into the alternator rotor coil is about zero, there is little, if any alternator counter torque on the engine and the rectified alternator output bridge diodes are backed biased and provide no current. Accordingly, the run battery will discharge to operate the vehicle load. During this discharge, the absence of the alternator counter torque results in improved fuel economy.
However, when the state of charge of the run battery falls to the second charge level, which corresponds to a low charge (deep discharge) level that will not damage the run battery, the control circuit/voltage regulator controls the battery charging device to provide the third output voltage. The third output voltage is then used to provide power for the vehicle load.
The third output voltage level may be selected as follows. It may be a level that will power the vehicle load and maintain the run battery at the second charge level. This selected level may be adjusted to prevent any further reduction in the state of charge of the run battery. In this case, the third output voltage may be on the order of 12 volts, as adjusted for ambient temperature conditions. Alternatively, the third output voltage may be a level that will power the vehicle level and recharge the run battery to a fully charged state, e.g., a voltage between 13 and 14.6 volts dc, as a function of ambient temperature. Once the run battery is recharged, it is allowed to discharge down to the second charge level, during which time the vehicle loads are again run exclusively off the run battery. Thus, whenever the alternator output voltage is reduced from the conventional full charging state, the alternator counter torque on the engine is less and there is improved fuel economy.
In all cases, the run battery is preferably recharged using a conventional battery charger which is powered from an external line source, e.g., a 220 or 115 volt ac line power supply. This permits replacing the amp-hour charge that was removed from the run battery by the vehicle loads with a source of electricity external to the vehicle. The external electricity source typically costs less per unit of energy than petroleum and alcohol based fuels and avoids consuming the incremental fuel that was saved during discharge of the run battery to generate the power needed to recharge the run battery. Such a battery charger may be mounted on or off the vehicle.
In another mode of operation, after the start battery and run batteries are recharged, the start battery is switched out and the battery charging device is operated to provide a fifth output voltage level and current for operating the vehicle accessory load. The fifth output voltage level is preferably selected to provide just enough current to operate the vehicle accessory loads, e.g., 12 volts for a 12-volt system and also applies a trickle charge current on the run battery. This mode also reduces the energy consumed as compared to prior voltage regulator start battery alternator systems that always produced more voltage than was required by the vehicle loads.
Switches and control circuits may be used to control automatically and/or manually the battery charging device and to connect selectively the battery charging device to one or both of the run and start batteries, and to provide the desired output voltage(s) and current(s) to recharge the batteries, singly or jointly, to operate the accessory and non accessory loads. A microprocessor may be used to control the various battery state of charge monitors, control circuits, and switches. Alternatively, a logic circuit network or a state machine comprising discrete and solid state components may be used as a control circuit. In addition, an operator display and manual switching system may be used.
Another aspect of this invention concerns providing a switch to connect one battery in place of the other battery if one of the batteries should fail to hold an adequate charge, and to use both batteries in parallel or in series when conditions so require. This is particularly useful in very cold weather when an additional source of start current is desired, and where one battery either fails or is not fully recharged before the engine is turned off.
Optionally, a measure of the amplitude and direction of the current flow into or out of the run battery or the start battery may be included for decision making purposes in selecting a voltage level. A large start battery discharge current may confirm a starting operation and raise the alternator output voltage level. An increased flow of current out of the run battery, i.e., a load current that might deplete charge from the run battery if the trickle charging voltage was maintained, could result in raising the trickle charging voltage, the load current and the battery state of charge.
Preferably, the start battery is a conventional automotive battery having thin cell plates and the run battery is a deep discharge, marine or cycle-proof battery. Such run batteries have thick cell plates and can be deep discharged to levels repeatedly, without seriously shortening their useful life. The thick plate construction also allows longer operation as an energy source than comparable thin cell plate starter batteries. However, run batteries typically cannot develop the high discharge currents suitable for starting the engine of an automotive vehicle. Other types of run batteries which are capable of repeated deep discharge are becoming available and may be used. For example, Ford Motor Company has announced such a high charge storage run battery for use in its forthcoming electric vehicle. Other batteries, such as sodium sulphur batteries having increased amp-hour ratings, as compared to lead acid batteries, also may be used. Further, when deemed appropriate, the size of run battery 20 may be reduced to a five cell battery to have a 12 volt rating or increased to 24-25 volt with a DC/DC convertor to increase the time for running off run battery 20, and to reduce the size of the alternator.
Advantageously also, it has been discovered that a fuel and cost savings can be achieved by the reduced alternator mechanical load on the engine and lower fuel consumption whenever, and to the extent that, the alternator field current is decreased to back bias the output rectifier diodes. Another advantage results from recharging a discharged battery using lower cost electricity from a source external to the vehicle.
Preferably, the state of charge of each battery used is monitored by a battery state of charge (BSOC) monitoring circuit channel. Any device capable of reliably integrating the net charge over time may be used. Preferably, the BSOC circuit includes a section of the battery return cable as a shunt or a shunt resistor in series with the battery negative terminal and a circuit having a very large capacitance for integrating the current through the shunt continuously. See e.e., the circuits disclosed in the aforementioned U.S. Pat. No. 4,968,941 and copending and commonly assigned U.S. patent applications Ser. Nos. 07/607,237 and 07/919,011, which patent and applications are expressly incorporated herein by reference in their entirety.
Another aspect of the invention concerns apparatus and methods for controlling the charging voltage level applied to a battery in an automotive vehicle in response to the deceleration of the vehicle. Broadly, this aspect of the invention concerns sensing the deceleration of a vehicle and causing the battery charging device to produce a high level charging voltage for rapidly recharging a battery during deceleration. When the vehicle is decelerating, the alternator is driven by the momentum of the vehicle turning the wheels, drive shaft, and, hence, the engine, and not by the engine burning fuel. Thus, during deceleration some of the energy stored in the momentum of the vehicle can be converted by the alternator to energy which is stored in the run battery.
Accordingly, during deceleration events, the control current to the alternator rotor is increased. This raises the alternator output voltage and results in an increased resistance to rotation of the alternator rotor coil. As a result, the charge on the battery is rapidly increased without consuming incremental fuel to do so. Another advantage is that the increased alternator counter torque load on the engine aids in slowing the vehicle without increased brake wear or effort.
The deceleration feature is particularly useful in stop and go traffic such that the battery charging device is turned off during steady state and accelerating driving conditions and is turned on to provide a high charging voltage during deceleration. The recharging during each deceleration will effectively prolong the time the vehicle can operate solely off the run battery. It also is useful when operating the battery charging device at a charging voltage just to maintain a charge on the run battery, for recharging start batteries, whether in the two battery charging system or a single battery charging system.
During the onset of deceleration, it may be desirable to ramp the control signal to raise the battery charging device output to a high voltage to minimize slippage and wear on the alternator. A switch may be provided to disable temporarily the deceleration feature when desired so that, for example, a driver can coast.
The various aspects of the invention are not limited to battery charging systems for automotive vehicles. They are applicable to any apparatus having a start battery that consumes energy to charge an electrical energy storage device that is connected to operate an electrical load or device, including without limitation, electrically starting combustion engines such as a generator for household (or industrial) current, a gas operated lawn mower, a powered vehicle or device, aircraft, spacecraft, watercraft, emergency lighting or power plants.
A further aspect of the invention provides a battery which provides a very high current to a heating coil of an electrically heated catalytic converter (EHC) unit which performs the emission control functions of a standard catalytic converter that is heated by the engine. This battery is referred to as an xe2x80x9cEHCxe2x80x9d battery or a xe2x80x9cstoragexe2x80x9d battery. The EHC unit may be a small catalytic converter that is placed in series with a standard catalytic converter, or it may be incorporated into an otherwise standard catalytic converter by, for example, the introduction of suitable heating coils as a part of the catalytic converter unit.
In operation, the EHC battery is switched, for about 20 seconds, to the EHC unit heater coil during the vehicle start operation. This provides a very high discharge current at a selected level, on the order of 500 to 650 amps, preferably 600 amps. The current discharge is high enough for the heater coil to heat rapidly at the EHC unit to its effective operating temperature and maintain it there during the heating period. The EHC battery may be disconnected after a preset time period, after the engine temperature exceeds a selected threshold, or when the state of charge of the EHC battery falls to a selected charge level. Further, the EHC battery may be switched to the EHC heater until the engine temperature is suitably high. This provides for preheating the catalytic converter so that it reaches an effective operating temperature sooner than conventional catalytic converter systems, which rely solely on engine temperature to heat the catalytic converter. Advantageously, by preheating the catalytic converter electrically, vehicle emissions are substantially reduced during vehicle starting, particularly in cold operating conditions. A third BSOC circuit channel could be used to monitor the EHC battery state of charge. If a BSOC channel is used, the control circuit is preferably responsive to the sensed EHC battery state of change (with appropriate switches) to recharge the EHC battery if its charge level is below the predetermined level. Provision also is made to recharge the ERC battery with an on or off-board battery charger from a source of 220 or 115 volt ac line power.
Furthermore, the EHC battery may be periodically switched to the EHC heater coil during operating conditions whenever the engine operating temperature is insufficient to heat the catalytic converter to its effective operating condition. This mode of operation may be selectively enabled or disabled, and the EHC battery may be recharged whenever its state of charge falls below a selected charge threshold.
Although each of the EHC battery system, the two-battery charge system, and the deceleration recharging system may be used separately, they are preferably combined to provide a more fuel efficient and reduced emission automotive vehicle.